泛北极多年冻土及重大线性工程稳定性状况

泛北极是中国“一带一路”倡议的主要合作示范区域,已有的重大线性工程及新的基础设施建设均面临着与多年冻土相关的冻融灾害及工程病害问题。在全球气候变暖及人类活动增强的背景下,泛北极多年冻土主要呈现地温升高、活动层厚度增加趋势,且低温多年冻土地温升高更加明显,20世纪70年代以来年平均地温(MAGT)升温最高可达3℃;自北向南多年冻土活动层厚度增加,且增厚趋势趋于明显,在俄蒙边境地区活动层厚度增速为3~5 cm·年-1。多年冻土退化诱发系列与热喀斯特过程相关的地质灾害,主要包括热喀斯特滑坡与热喀斯特湖,且灾害数量急剧增加,如加拿大Banks Island地区1984~2015年热喀斯特滑坡数量增加了约60倍。在多年冻土退化、热稳定性降低的背景下,泛北极铁路、公路和管道等重大线性工程出现了沉陷、裂缝等不同类型、不同程度的病害,整体上多年冻土区道路工程病害率大于30%。热融灾害及工程病害的发育均与气候及岩土、冻土条件相关,但工程病害还与工程运营期限、工程结构形式密切关联。对比泛北极道路、管道等线性工程状况及其与工程结构的关系,以及病害特征和防治措施效果,表明基于保护冻土的“主动冷却”设计原则依然是多年冻土区工程设计的主导思想。     

冻土冻融对地下水的影响:以祁连山多年冻土区大通河谷融区为例

冻土区地下水的形成、补给、径流、排泄方式以及地球化学特征受到冻土分布及其季节性冻融过程的强烈影响。以地处祁连山多年冻土区的大通河谷融区为典型研究区,基于钻探、坑探和地球物理工作查明了区内冻土特征和分布情况;结合水文地质观测及抽水试验,分析了研究区河流融区内地下水的赋存条件,深入研究了区内冻土冻融过程影响下地下水的水文地质和水化学特征,认为冻土冻融过程决定了研究区的地质和水文地质条件,控制着地下水的补给、径流、排泄方式,特别是对地下水质有优化作用——冻土区地下水质明显优于非冻土区。冻土区地下水成因和赋存条件研究对于其开发利用有重要意义。      

冻土斜坡模型试验相似分析

南水北调工程、青藏铁路建设工程等一系列工程的实施,将进一步影响和加剧青藏高原多年冻土区斜坡稳定性问题,冻土区边坡开挖及斜坡稳定性是工程活动中必须解决的问题之一,冻土斜坡稳定性研究在国内尚属空白。通过相似模型试验对高原多年冻土区斜坡在自然和人类活动影响下的失稳机制和活动规律进行分析,是开展研究的重要手段。根据相似理论第一定律,对冻土斜坡模型试验进行了相似分析,应用积分类比法推导并建立了冻土斜坡模型试验的相似指标和相似判据,得出在用原状土作模型介质时,6个相似常数减少为2个相似常数,即cτ和cl。模型与原型的时间比例尺是由几何比例尺决定的,即cτ=c2l,仅有一个相似参数为自变量,另一个为因变量。据此对青藏高原多年冻土区青藏公路沿线K3035处冻土斜坡进行了相似模型设计和冻融模型试验。模型再现了K3035处7°斜坡在4个冻融循环条件下,坡体中部(水平、垂向)4#位移伸张计质点位移曲线随时间的变化特征。实验表明,斜坡土体中部在第一次冻融循环中已有滑动迹象,随着滑坎进一步后退和靠近观测基准点,必然出现一次较大的位移,直至周边土体出现滑塌为止。模型试验结果与现场观测资料相比较是令人满意的。     

气候变暖影响中国重大工程安全

中国气象局局长、中国科学院院士秦大河日前指出，极端气候变化对中国重大工程的安全运行可能产生一定影响。他说，气候变化可能增加长江流域上游降水，引发三峡库区泥石流、滑坡等地质灾害；而未来青藏高原气温有可能变暖，青藏铁路沿线多年冻土可能会进一步退化，从而影响某些地段铁路路基的稳定性。     

青藏高原多年冻土概论

本文较系统地阐述了青藏高原多年冻土的地带性规律、冻土构造以及融区的类型和分布特征,详细论述了不同作用下形成的冻土(冰缘)地貌,并对青藏高原的冰缘期进行了初步划分与对比。     

多年冻土区河流溶解性有机碳输出的研究进展

多年冻土区河流中溶解性有机碳（DOC）的输出对全球碳循环有着重要贡献，是全球气候变化研究的热点。当前研究主要集中在2个方面:多年冻土区河流DOC输出的时空特征及其影响因素；多年冻土区河流DOC输出对气候变暖和冻土退化的响应。研究表明，河流中DOC的浓度、通量、化学组分等主要受流域内水的流动路径、滞留时间及路径上潜在DOC源的特征控制，而多年冻土的分布及其季节性融冻循环对上述因素有显著影响，进而控制多年冻土区河流DOC的输出规律。气候变暖可从3个方面对多年冻土区河流DOC输出产生影响:①造成多年冻土退化，使地下水的流动路径变深和滞留时间增长，导致河流的DOC输出量降低；②使多年冻土中储存的老有机碳释放，导致河流的DOC输出量增高；③改善深部土壤的通气和温度条件，促进土壤微生物活性，进而影响河流DOC的输出量和化学特征。今后，有3个方面的研究需要加强:①中、低纬度高海拔冻土区河流DOC的输出规律及其与流域水文过程的关系；②小型源头河流DOC输出的对比与控制性试验；③冻土区地下水流过程的精细刻画和潜在有机碳源的直接探测。      

青藏铁路通风路堤室内模型试验研究

正在建设中的青藏铁路即将穿越 5 5 0km的多年冻土区 ,冻土问题是青藏铁路面临的首要工程问题。出于铁路建设中保护冻土的原则 ,对通风路堤这一新的、主动保护冻土的路堤结构形式进行了几何相似比为 1∶4的大型室内试验 ,试验所得的路堤土体温度场分布及土体温度的变化结果表明 ,通风路堤能够有效地降低路堤土体的温度 ,从而达到保护天然地基冻土的目的。但是 ,温度场的分布在通风路堤内并不对称 ,及沿路堤中轴线的两侧左右不对称 ,这样可能会影响到下伏冻土温度的差异 ,从而引起不均匀冻胀、沉降变形。另一方面 ,暖季较高的气温条件下 ,通风管两端的进出口需要堵塞或关闭 ,以免造成土体吸热量较多而引起较大的沉降 ,但由于青藏高原很短的融化期 ,这一影响还有待现场试验工程的验证。     

基于GRACE RL06数据探测三江源地区陆地水储量变化

利用CSR最新发布的GRACE RL06数据反演2006~2015年三江源地区陆地水储量的时空变化,并结合GLDAS水文模型、TRMM降水数据及地表冻融数据进行对比分析。结果表明,三江源地区的陆地水和地表水在2006~2015年的变化趋势分别为5.2±1.2 mm/a和-3.8±0.9 mm/a;降水与陆地水的变化密切相关,也是造成陆地水储量呈季节性变化的主要原因;冻土作为特殊的蓄水层,影响着三江源地区地表水与地下水之间的水力联系,冻土活动可能造成GRACE与GLDAS水储量之间的差异;根据GRACE与GLDAS水储量在空间趋势上的差异推测,三江源地区高原多年冻土退化,活动层增厚。     

高山湖盆区特殊性工程岩土

研究了国道219线新疆接西藏段阿克赛钦湖区新生代高山湖盆的构造演化及沉积物岩相分带,利用地质调查、钻探、物探、试验等工作成果,对公路展布带及地基影响深度范围内的特殊性工程盐渍土的盐渍化类型、程度、盐胀性,冻土的类型、融沉性、盐渍化冻土进行了研究与分类。综合评价了特殊土的工程性能和对公路工程的影响程度,为改建公路的选线和路基设计提供了依据,并提出了经济合理、可行的特殊土工程整治措施。     

南水北调西线叶青—勒那曲引水线工程地质条件分段评价

叶青—勒那曲引水线路根据地质构造、地貌特征、物理地质现象,共划分六个区段。德曲段:山脊寒冻风化碎石坡型,山坡融冻泥流及顺河断层发育;解吾曲下段:冻土沼泽发育,南北构造活动较强烈,区域稳定性及边坡稳定性较差;解吾曲上游段;山区和丘陵区断裂发育,在喜山末期有强烈的活动,滑坡、冰丘等不良地质现象极为发育;玛尕曲—洛曲南段:厚层地下冰发育,近期活动断裂明显;洛曲南岸—多曲东岸段:缓坡区有厚层地下冰,多年冻土布满全段;多曲东岸—万龙湾尕玛下游段:近代断裂活动明显,区域稳定性较差。     

Characteristics of thawed interlayer and its effect on embankment settlement along the Qinghai-Tibet Railway in permafrost regions

The formation of thawed interlayer beneath embankment can result in embankment settlement in permafrost regions. Based on the data on ground temperatures and deformations beneath the embankment, observed in-situ along the Qinghai-Tibet Railway in permafrost regions from 2006 to 2013, characteristics of the thawed interlayer beneath the embankment and its influence on the embankment settlement are studied. The results indicate that the thawed interlayer hardly forms beneath the natural field, and beneath the embankments from the Qinghai-Tibet Railway the thawed interlayer develops widely, and it can be refrozen totally in the regions with lower mean annual ground temperature, and developed further in the regions with higher mean annual ground temperature. The thawed interlayer is closely related to the embankment settlement. The ice content of permafrost underlying the thawed interlayer influences the settlement of embankment. The higher the ice content is, the larger the settlement is, and vice versa. The increase in thickness of thawed interlayer mainly results from the decline of artificial permafrost table in high-temperature permafrost regions.     

Variations in the northern permafrost boundary over the last four decades in the Xidatan region,Qinghai–Tibet Plateau

The distribution and variations of permafrost in the Xidatan region, the northern permafrost boundary of the Qinghai-Tibet Plateau, were examined and analyzed using ground penetrating radar(GPR), borehole drilling, and thermal monitoring data. Results from GPR profiles together with borehole verification indicate that the lowest elevation limit of permafrost occurrence is 4369 m above sea level in 2012. Compared to previous studies, the maximal rise of permafrost limit is 28 m from 1975 to 2012. The total area of permafrost in the study region has been decreased by 13.8%. One of the two previously existed permafrost islands has disappeared and second one has reduced by 76% in area during the past ~40 years. In addition, the ground temperature in the Xidatan region has increased from 2012 to 2016, with a mean warming rate of ~0.004℃ a~(-1) and ~0.003℃ a~(-1) at the depths of 6 and 15 m, respectively. The rising of permafrost limit in the Xidatan region is mainly due to globalwarming. However, some non-climatic factors such as hydrologic processes and anthropic disturbances have also induced permafrost degradation. If the air temperature continues to increase, the northern permafrost boundary in the Qinghai-Tibet Plateau may continue rising in the future.     

An Estimation of Ground Ice Volumes in Permafrost Layers in Northeastern Qinghai-Tibet Plateau,China

The ground ice content in permafrost serves as one of the dominant properties of permafrost for the study of global climate change, ecology, hydrology and engineering construction in cold regions. This paper initially attempts to assess the ground ice volume in permafrost layers on the Qinghai-Tibet Plateau by considering landform types, the corresponding lithological composition, and the measured water content in various regions. An approximation demonstrating the existence of many similarities in lithological composition and water content within a unified landform was established during the calculations. Considerable knowledge of the case study area, here called the Source Area of the Yellow(Huanghe) River(SAYR) in the northeastern Qinghai-Tibet Plateau, has been accumulated related to permafrost and fresh water resources during the past 40 years. Considering the permafrost distribution, extent, spatial distribution of landform types, the ground ice volume at the depths of 3.0–10.0 m below the ground surface was estimated based on the data of 101 boreholes from field observations and geological surveys in different types of landforms in the permafrost region of the SAYR. The total ground ice volume in permafrost layers at the depths of 3.0–10.0 m was approximately(51.68 ± 18.81) km~3, and the ground ice volume per unit volume was(0.31 ± 0.11) m~3/m~3. In the horizontal direction, the ground ice content was higher in the landforms of lacustrine-marshland plains and alluvial-lacustrine plains, and the lower ground ice content was distributed in the erosional platforms and alluvial-proluvial plains. In the vertical direction, the volume of ground ice was relatively high in the top layers(especially near the permafrost table) and at the depths of 7.0–8.0 m. This calculation method will be used in the other areas when the necessary information is available, including landform type, borehole data, and measured water content.     

Cryostructures and ground ice content in ice-rich permafrost area of the Qinghai-Tibet Plateau with Computed Tomography Scanning

Permafrost is an important part of the cryosphere, playing an integral role in the hydrologic cycle, ecology, and influencing human activity. Melting of ground ice can drastically change landscapes and associated thaw subsidence may induce instability of infrastructure. The terrain conditions on the Qinghai-Tibet Plateau are complex, and the spatial distribution of ground ice is highly variable, so knowledge of its abundance and variability is required for impact assessments relating to the degradation of permafrost. This study examined 55 permafrost samples from warm, ice-rich permafrost region in Beiluhe Basin, Qinghai-Tibet Plateau. The samples were examined using Computed Tomography scanning, and the ice content and cryostructure were determined. The results indicated that: 1) variation in volumetric ice content was considerable(0%-70%), with a mean value of 17%; 2) seven cryostructures were identified, including crustal, vein, lenticular, ataxitic, reticulate and layered cryostructure; 3) volumetric ice content varied by cryostructure, with the highest associated with layered and ataxitic cryostructures. Volumetric ice contents were lowest for samples with pore and lenticular cryostructures. This work provides detailed ground ice content and will be helpful for assessing thaw subsidence and infrastructure stability on Qinghai-Tibet Plateau.     

Modeling regional and local-scale permafrost distribution in Qinghai-Tibet Plateau using equivalent-elevation method

This study proposes an equivalent-elevation method to evaluate the integrated effects of latitude and elevation on regional and local-scale permafrost distribution in the Qinghai-Tibet Plateau,and to model the general permafrost-distribution patterns in regional and local-scale area.It is found that the Gaussian curve―an empirical model describing the relation between variations of altitudinal permafrost lower limit (PLL) and latitude in the Northern Hemisphere―could be applied in regional-and local-scale areas in the Qinghai-Tibet Plateau in a latitude-sensitive interval of 30°-50°N.The curve was then used to evaluate the latitudinal effect on permafrost distribution through transforming the latitudinal effect into a kind of altitudinal difference of PLL.This study then calculated the local equivalent-elevation value by overlaying the altitudinal difference of PLL onto real elevation at a certain location.The equivalent-elevation method was verified in an experimental subwatershed of the Qinghai-Tibet Plateau.However,feasibility of the method should be further tested in order to extend for future studies.The use of equivalent-elevation values can build a platform for comparing the regional general permafrost distribution in the plateau,and for basing further evaluations of local factors’ effects on regional permafrost distribution.     

Response of biomass spatial pattern of alpine vegetation to climate change in permafrost region of the Qinghai-Tibet Plateau,China

Alpine ecosystems in permafrost region are extremely sensitive to climate changes.To determine spatial pattern variations in alpine meadow and alpine steppe biomass dynamics in the permafrost region of the Qinghai-Tibet Plateau,China,calibrated with historical datasets of above-ground biomass production within the permafrost region's two main ecosystems,an ecosystem-biomass model was developed by employing empirical spatialdistribution models of the study region's precipitation,air temperature and soil temperature.This model was then successfully used to simulate the spatio-temporal variations in annual alpine ecosystem biomass production under climate change.For a 0.44°C decade-1 rise in air temperature,the model predicted that the biomasses of alpine meadow and alpine steppe remained roughly the same if annual precipitation increased by 8 mm per decade-1,but the biomasses were decreased by 2.7% and 2.4%,respectively if precipitation was constant.For a 2.2°C decade-1 rise in air temperature coupled with a 12 mm decade-1 rise in precipitation,the model predicted that the biomass of alpine meadow was unchanged or slightly increased,while that of alpine steppe was increased by 5.2%.However,in the absence of any rise in precipitation,the model predicted 6.8% and 4.6% declines in alpine meadow and alpine steppe biomasses,respectively.The response of alpine steppe biomass to the rising air temperatures and precipitation was significantly lesser and greater,respectively than that of alpine meadow biomass.A better understanding of the difference in alpine ecosystem biomass production under climate change is greatly significant with respect to the influence of climate change on the carbon and water cycles in the permafrost regions of the Qinghai-Tibet Plateau.     

Role of permafrost in resilience of social-ecological system and its spatio-temporal dynamics in the source regions of Yangtze and Yellow Rivers

Permafrost is one of the key components of terrestrial ecosystem in cold regions. In the context of climate change, few studies have investigated resilience of social ecological system(SER) from the perspective of permafrost that restricts the hydrothermal condition of alpine grassland ecosystem. In this paper, based on the structural dynamics, we developed the numerical model for the SER in the permafrost regions of the source of Yangtze and Yellow Rivers, analyzed the spatial-temporal characteristics and sensitivity of the SER, and estimated the effect of permafrost change on the SER. The results indicate that: 1) the SER has an increasing trend, especially after 1997, which is the joint effect of precipitation, temperature, NPP and ecological conservation projects; 2) the SER shows the spatial feature of high in southeast and low in northwest,which is consistent with the variation trends of high southeast and low northwest for the precipitation, temperature and NPP, and low southeast and high northwest for the altitude; 3) the high sensitive regions of SER to the permafrost change have gradually transited from the island distribution to zonal and planar distribution since 1980, moreover, the sensitive degree has gradually reduced; relatively, the sensitivity has high value in the north and south, and low value in the south and east; 4) the thickness of permafrost active layer shows a highly negative correlation with the SER. The contribution rate of permafrost change to the SER is-4.3%, that is, once the thickness of permafrost active layer increases 1 unit, the SER would decrease 0.04 units.     

Thermal state of soils in the active layer and underlain permafrost at the kilometer post 304 site along the China-Russia Crude Oil Pipeline

On-site monitoring is very important for understanding formation mechanisms of frost hazards frequently occurring in pipeline foundation soils and for designing and deploying according mitigative measures in permafrost regions.Significant thaw subsidence of ground surfaces along the ChinaRussia Crude Oil Pipeline(CRCOP) from Mo'he to Daqing,Heilongjiang Province,Northeast China have been observed at some segments underlain by ice-rich warm(1.0°C) permafrost since the official operation in January 2011.Recent monitoring results of the thermal states of foundation soils at the kilometer post(KP) 304 site along the CRCOP are presented in this paper.The results indicate that during the period from 2012 to 2014,shallow soils(at the depths from0.8 to 4.0 m from ground surface) has warmed by approximately 1.0°C in the lateral range of 1.2 to 2.1 maway from the pipeline axis,and deeper permafrost(such as at the depth of 15 m,or the depth of zero annual amplitude of ground temperatures) by 0.08°C per year 4 m away from the pipe axis,and 0.07°C per year 5 m away from the pipeline axis.The results indicate an all-season talik has developed around and along the CRCOP.The thaw bulb,with a faster lateral expansion(compared with the vertical growth),enlarges in summer and shrinks in winter.This research will provide important references and bases for evaluating thermal influences of warm pipeline on permafrost and for design,construction,operation and maintenance of pipelines in permafrost regions.     

Mapping the vegetation distribution of the permafrost zone on the Qinghai-Tibet Plateau

In this paper,an updated vegetation map of the permafrost zone in the Qinghai-Tibet Plateau(QTP) was delineated.The vegetation map model was extracted from vegetation sampling with remote sensing(RS) datasets by decision tree method.The spatial resolution of the map is 1 km×1 km,and in it the alpine swamp meadow is firstly distinguished in the high-altitude areas.The results showed that the total vegetated area in the permafrost zone of the QTP is 1,201,751 km~2.In the vegetated region,50,260 km~2 is the areas of alpine swamp meadow,583,909 km~2 for alpine meadow,332,754 km~2 for alpine steppe,and 234,828 km~2 for alpine desert.This updated vegetation map in permafrost zone of QTP could provide more details about the distribution of alpine vegetation types for studying the vegetation mechanisms in the land surface processes of highaltitude areas.     

Temperature monitoring from 2012 to 2019 in central part of Suntar-Khayat Ridge,Russia

In recent decades, research of the Alps, Qinghai-Tibet Plateau, and Cordillera have made great progress in understanding the phenomenon of permafrost. For the most part, this has been made possible due to temperature monitoring. However, the permafrost parameters in an area of more than 2 million square km of the mountainous regions of northeast Asia, for the most part, remain a blank spot in the scientific community. Due to the lack and insufficiency of factual materials, in 2012 the P.I. Melnikov Permafrost Institute began to take temperature measurements in the upper part of the permafrost in the central part of the VerkhoyanKolyma uplands, namely the Suntar-Khayat ridge. The article describes the temperature characteristics of air, surface and rocks of the active layer in the range of heights from 850 to 1821 m, in various landscape and topographic elements. For the observation period from 2012 to 2019, we obtained information on temperatures in the soils of the active layer at depths of 1 m, 3 m, 4 m, and 5 m and also air and surface temperature parameters. The availability of data on automated monitoring of rock temperatures in the active layer and the upper horizons of the layer of annual heat rotations made it possible to substantiate the most typical conditions of the temperature conditions of the permafrost zone of the characterized region. The parameters of permafrost existence and development are in favorable conditions. This is shown in the analysis of temperature data of air, surface and active layer. Soil temperatures in the active layer of annual heat rotations are most clearly represented at a depth of 1 m. Currently, on the territory of the mountain regions of Eastern Siberia, there are no more such sites for monitoring the temperature regime of soils. Information on the permafrost parameters in the region will allow us to begin the process of creating new models or checking existing forecasts and the distribution of the temperature pattern. It will also make it possible to evaluate the response of sensitive and vulnerable frozen soils of mountain regions to climate change.